MXPA99008505A - Method for measuring the level of carboxylate anion in engine coolant and test kit for carrying out the method - Google Patents

Abstract

Se proporciona un método colorimetrico para determinar la presencia o ausencia de un nivel de unión carboxilato. inhibidor de la corrosión, en refrigerante acuoso para motor utilizado.

Description

METHOD FOR MEASURING THE CARBOXYLATE ANION LEVEL IN REFRIGERANT FOR ENGINES AND TEST EQUIPMENT TO PERFORM THE METHOD BACKGROUND OF THE INVENTION This invention relates to a method for measuring the carboxylate anion present in refrigerants used for automobile and heavy-duty engines where it functions as a corrosion inhibitor to a test equipment to perform a method. Coolant systems for automobile engines contain a variety of metals and metal alloys such as copper, solder, brass, steel, cast iron, aluminum and magnesium. The vulnerability of these metals to corrosive attack is high due to the presence of corrosive liquids and different ions, as well as high temperatures, pressures and flow rates characteristic of engine cooling systems. The presence of corrosion products within a refrigerant system can also interfere with the transfer of heat from the combustion chambers of the engine that can cause the engine to overheat and the engine components to fail. Corrosion inhibitors are commonly added to engine coolants, for example, silicates are added to provide protection to aluminum, nitrites are added for protection to molten iron and azoles can be added for protection of copper and brass against corrosion, and to help in the protection of iron and zero. All corrosion inhibitors used in antifreeze / coolant formulations for automobiles are gradually depleted by use. The life expectancy of most refrigerants is approximately 1 to 3 years due to the progressive depletion of the corrosion inhibiting component (s). The carboxylic acids in the formula of their salts have been incorporated into engine coolants in order to provide a greater degree of corrosion protection than other known types of corrosion inhibitors. The carboxylates are superior due to their slower depletion rates compared to other corrosion inhibitors. The life expectancy of refrigerants containing carboxylate is usually 5 years or more. For proper maintenance of the coolant, the engine operator must routinely check the coolant levels to determine that it is providing protection at the boiling point and proper freezing. To maintain adequate levels of the corrosion inhibitor, it is also essential that the engine operator continually check the levels of the corrosion inhibitor and renew the corrosion inhibitor as circumstances require. The replacement of the complete refrigerant may be necessary when deterioration or severe contamination occurs. Rapid test methods are available to determine the content of the corrosion inhibitor, for example, nitrite content, molybdate content, etc. of the engine coolant used which includes immersing a test strip in the coolant which produces a color change which may be related to the level of the corrosion inhibitor. A low reading for the corrosion inhibitor indicates that corrective action must be taken to restore protection, for example, the use of refrigerant additives as a supplement or extenders to re-establish specific levels of the corrosion inhibitor for sufficient protection. Test methods are also available to determine that the levels of the corrosion inhibitor are not too high when complementary cooling additives are used in order to restore levels of the corrosion inhibitor. During use, the carboxylate corrosion inhibitors are depleted at a slower rate than other known inhibitors but, over time, can be contaminated by dilution with other manufactured engine coolants or water after refilling the coolant. In order for the carboxylate corrosion inhibitors to provide adequate protection against corrosion, its levels in refrigerants used for engines and heavy duty must be periodically determined. The carboxylate anion present in the engine coolant used can be analyzed by a well-equipped laboratory using chromatographic techniques. However, these procedures are expensive and time consuming. Accordingly, there is a need for a non-expensive, rapid and reliable method for determining the carboxylate anion levels present in automotive and heavy-duty engine coolants that by itself allow to be performed in the field with a minimum of technical experience.

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for determining the presence or absence of a corrosion inhibiting level of carboxylate anion in coolant used for engine consisting of: a) obtaining a known quantity of engine coolant as a representative sample thereof, the sample containing a level of carboxylate anion to be determined; b) adding a certain amount of a aluminum cation source to the sample, the aluminum cation forms a complex with the carboxylate anion to form an insoluble aluminum-carboxylate complex, this cation-free aluminum being present in the sample when the level of carboxylate anion therein is below an effective, corrosion inhibiting amount, and there is no aluminum cation present in the sample when the carboxylate anion level is in the corrosion inhibiting effective amount; c) add a colorful indicator to the sample that forms an irreversibly colorful complex with any free aluminum cation present in it at a pH that originates from the colorful complex, with the sample adjusted within this pH if necessary to allow formation of the colorful complex; and d) observe the color of any complex that may have formed between the free aluminum cation and the color indicator to determine the level of the carboxylate anion in the sample, the sample being adjusted to a different pH if necessary to remove any color that may have resulted from the presence of excessively colored indicator in the sample. Further, in accordance with the present invention, portable test equipment, suitable for field use, is provided to perform the aforementioned colorimetric method in determining the level of carboxylate anion in refrigerants used in automotive and heavy-duty engines.

DESCRIPTION OF THE PREFERRED MODALITIES The corrosion inhibitors whose levels are determined according to the method of this invention are the alkali metal or ammonium salts of carboxylic acids which form an aluminum-carboxylate complex insoluble in the reaction with a cation source. aluminum. Examples of these alkali metal or ammonium salts are those of suberic acids, azelaic acid, undencadioic acid, dodecandioic acid, propionic acid, butyric acid, valeric acid, capric acid, ethylhexanoic acid, benzoic acid, para-butylbenzoic acid, cyclo-exancarboxylic acid and Similar. The preferred carboxylate corrosion inhibitor is an alkali metal ethylhexanoate, for example sodium ethylhexanoate, potassium ethylhexanoate, and the like. - A known quantity of the coolant used for automobile or heavy-duty engine is removed from the engine cooling system in order to provide a representative sample from which the content of the carboxylate anion is determined. In general, the amount of the refrigerant sample can vary from about 2 to about 100 g, and preferably from about 5 to about 30 g. A fixed amount of an aluminum cation source, for example, a standard solution of the aluminum cation, is then added to the sample. The precise amount of the aluminum cation will depend on the size of the refrigerant sample and the molar percent of the carboxylate anion needed for adequate protection against corrosion. It is possible to perform routine tests to provide standard solutions of the proper concentration of the aluminum cation for specific formulations of refrigerant. Aluminum cation sources suitable for preparing these standard solutions include soluble aluminum compounds such as chlorides, sulfates, nitrates, etc., of aluminum and its hydrates. It has been found that aluminum nitrate nonahydrate, Al (N03) 3 * 9H20, gives especially good results. After the addition of aluminum cation, the aluminum cation forms complex with the carboxylate anion to produce an insoluble aluminum-carboxylate complex. The content of the carboxylate anion in the refrigerant sample will determine the amount of the aluminum-carboxylate complex that forms. When the content of the carboxylate anion has decreased below a predetermined corrosion inhibiting effective amount, i.e., the situation resulting from excessive depletion of the carboxylate anion over time, the entire amount of carboxylate anion in the sample will complex with the Aluminum cation and some free aluminum cation will remain in the sample. The amount of free aluminum cation present in the sample is inversely related to its carboxylate anion content, so that when there is an effective corrosion inhibiting level of the carboxylate anion, there will be no free aluminum cation present in the refrigerant sample and, on the contrary, when there is insufficient carboxylate anion to provide a predetermined level of corrosion inhibition, aluminum cation will be present in the sample. Thus, when the content of carboxylate anion in the sample of the refrigerant is at an effective corrosion inhibiting level, the entire amount of added aluminum cation will form the complex with the carboxylate anion without free aluminum cation remaining in the sample. However, when the content of carboxylate anion has dropped below some predetermined level, there will be some amount of free aluminum cation present in the sample. After formation of the carboxylate, the sample will optionally be filtered to remove the insoluble complex particles thus providing a clean sample free of any of the suspended particles of the insoluble complex which could tend to obscure the color change that occurs when, more is described ahead, a colorful indicator is added to the sample. Although it is possible to use other techniques to remove the insoluole complex in aluminum carboxylate, for example, centrifugation after decanting the resulting clear liquid, filtration is a simple procedure that requires a minimum of equipment and as such is well suited for field use . Once the insoluble aluminum-carboxylate complex has been formed (and optionally separated from the refrigerant sample as described above), a color indicator complexing with the aluminum cation is added to the mixture. If there is free aluminum cation present in the sample which, as explained above, will be the case when the carboxylate content of the sample is below a predetermined corrosion inhibiting effective amount, the color indicator will form a colorful complex irreversible with the aluminum cation. However, if there is no aluminum cation present in the sample, such as when the content of the carboxylate anion is at a predetermined minimum level, effective as a corrosion inhibitor, the addition of the color indicator will not result in the formation of any complex indicator. color-aluminum.

Suitable color indicators that can be used herein are well known in the art and include hematoxylin, Eriochrome Cyanine R, aurintricarboxylic acid, Pantachrome Blue Black, R, Alizarin S, and the like. Hematoxylin produces clearly observable color changes when complexed with aluminum cations at an alkaline pH and is preferred for use herein. The concentration of the colorful indicator _ in the refrigerant sample may vary according to the type of engine coolant being tested. For example, in the case of hematoxylin, if the refrigerant does not contain a coloring component, then the concentration of hematoxylin will usually be in the range of about 0.005 to about 0.2 mg per g of refrigerant, and preferably from about 0.1 to about 0.15 mg per g of refrigerant. If the engine coolant contains a coloring coolant, then the amount of the color indicator should be increased due to the interference of the coloring component in the engine coolant with the color resulting from complexing of the color indicator with any free aluminum cation. The increased concentration of the color indicator will usually be in the range from about 0.2 to about 0.8 mg per g of refrigerant and, preferably from about 0.4 to about 0.6 mg per g of refrigerant. As noted above, hematoxylin forms an irreversible colorful complex with aluminum cation only at alkaline pH. Accordingly, it may be necessary to adjust the pH of the sample with a base, for example, for a pH greater than 7, and preferably for a pH of at least about 8 before or after the addition of the color indicator. Since excess hematoxylin itself produces color at alkaline pH, it may be necessary to acidify the refrigerant sample once the aluminum-color indicator complex is formed to remove or neutralize any color that may be due to the presence of hematoxylin in excess. Since the color change in the sample, which is realized by the formation of the aluminum-color indicator complex is irreversible, the subsequent acidification of the sample will not affect a change in color of the aluminum-color indicator complex but only it will eliminate the color that has been produced by the presence of excess hematoxylin at the previous alkaline pH. When it forms the complex with the aluminum cations and alkaline pH, hematoxylin provides a purple color that is clearly observed. If, after acidification of the sample, the purple color is absent (as will be the case when there is no free aluminum cation in the sample), it can be concluded that the carboxylate anion is present in the refrigerant at least a predetermined minimum amount for inhibit corrosion. However, when the purple color is observed (as will be the case when an aluminum-color indicator complex is formed), it can be concluded that the level of carboxylate anion in the refrigerant has dropped below a predetermined amount effective as an inhibitor of the corrosion and must be resupplied. Furthermore, it is within the scope of the invention to provide a kit containing the apparatus and / or reagents necessary to carry out the aforementioned test method in the field. A complete equipment will contain all the material and consumables to perform at least one test procedure. Thus, this equipment will include a device to obtain a refrigerant test sample, for example, a pipette or syringe to extract refrigerant, at least one device to maintain a precise volume of the refrigerant liquid, for example, a flask or test tube, a source of aluminum cation, for example an aluminum nitrate, preferably provided as a standard solution and a color indicator. Where the color indicator is hematoxylin or another indicator that produces color only at alkaline pH, the equipment will also contain a quantity of base with which the pH of the refrigerant sample can be adjusted to within the alkaline region, and an amount of acid with which to readjust the pH of the refrigerant sample to eliminate any color resulting from the presence of excess color indicator. Optionally, the equipment may contain a filtration device, for example, a funnel and filter paper to separate the suspended particles from the refrigerant sample after the formation of the insoluble aluminum-carboxylate complex. A partial test equipment shall include, at a minimum, the aforementioned source of the aluminum cation and color indicator. The following examples are illustrative of the method of this invention.

EXAMPLE 1 This example illustrates the reproducible nature of the reaction of aluminum cation and ethylhexanoate anion in a wide range of compositions in solution. A standard solution of the aluminum cation, Al + 3, was prepared by dissolving 4,006 g of aluminum nitrate nonahydrate (Al (N03) 3 * 9H20) in 147.5 g of deionized water.

Five more mixtures were prepared by adding aliquots of Havoline Extended Life antifreeze / coolant (refrigerant A) to the aluminum standard solutions and diluting with deionized water. The formulation of coolant A used in this example was identical to that found in the Havoline Extended Life antifreeze / coolant trade available from Texaco Lubricant Company, except that it contained no antifoam or dye component. Coolant A was formulated with ethylhexanoic acid which was converted in situ in the presence of the potassium hydroxide component to form potassium ethylhexanoate, the active corrosion inhibitor. The partial composition of refrigerant A is set forth in Table 1 as follows: Table 1: composition of refrigerant A Component Quantity,% by weight Potassium ethylhexanoate 3.26 * Anti-foam dye - Acehexanoic acid; present in ethylene glycol, The complete composition of the aluminum-refrigerant A mixtures are as follows: Table 2: Mixtures of aluminum-refrigerant A Mixture Weight of solutions Coolant weight Water weight Al pattern number, (g) A, (g) deionized, (g) 1 20.0 9.5 20.5 2 20.0 7.6 22.4 3 20.0 6.7 23.4 4 20.0 5.7 24.3 5 20.1 4.8 25.3 For the five samples, aluminum-ethylhexanoate precipitate formation was observed. All the samples were then filtered to eliminate the precipitate and analyzed for the content of aluminum and ethylhexanoate. Table 2 summarizes the elemental compositions of each aluminum-ethylhexanoate solution calculated on the basis of the added components (initial composition) and measured by analysis after the reaction of the cation aluminum (Al) and anion ethylhexanoate (EH) (final composition).

Table 3: Concentrations of aluminum and ethylhexanoate (moles / liter) before and after the reaction and filtration Solution to EH At the end EH final Ca ammbbiioo in Change in initial initial molar ratio To L EH of the change EH / A1 1 0.0213 0.0428 0 < 0.007 0.0213 > 0.0358 > 1.67 2 0.0213 0.0341 0.00204 0.01926 0.0341 1.771 3 0.0213 0.0298 0.00407 0 0.01723 0.0341 1.771 4 0.0123 0.0256 0.00641 0 0.01489 0.256 1.72 5 0.0123 0.0123 0.00930 0 0.012 0.213 1.775 From the results mentioned in Table 3, it is shown that the amount of ethylhexanoate anion that reacts with the aluminum cation is constant as indicated by the change in the molar ratio EH / Al and the averages around 1.75 moles of ethylhexanoate anion consumed per mole of aluminum cation consumed by solutions Nos. 2-5. For solution No. 1, the EH concentration was too low for an accurate measurement. Thus, in a wide range of refrigerant concentrations, the stoichiometry of the aluminum and EH reaction remains constant. (i: Al + 1.75 EH Al (EH) 1.75 Based on this stoichiometry, it is possible to predict within experimental error, the composition of the final reaction mixture if the amounts of aluminum cation and ethylhexanoate anion in the initial mixture are known. (2) At the thin end? - Alinicial ~ (EHin c al / 1. 75) Table 4 below presents the results for hypothetical mixtures of equal volumes of solutions of aluminum cation and ethylhexanoate anion.

Table 4: Prognosis of the compositions resulting from the solution reaction of cation1 aluminum with different solutions of anion hetilhexanoato Molar ratio Initial concentration of the initial concentration Final target concentration: EH / Al cation Al (moles / liter) of predicted EH (moles / liter) of the cation Al (moles / liter) 5.0 1.0 5.0 0.0 3.0 1.0 3.0 0.0 2.0 1.0 2.0 0.0 1.6 1.0 1.6 0.09 1.4 1.0 1.4 0.20 1.2 1.0 1.2 0.31 1.0 1.0 1.0 0.43 0.0 1.0 0.0 1.0 In this way, when the initial concentration of the ethylhexanoate anion is less than 1.75 moles / liter, the free aluminum cation will be present in the final reaction mixture. In this example, an initial concentration for the aluminum ion was arbitrarily selected. In practice, the initial concentration of the aluminum cation can be chosen such that the aluminum cation is present in the final solution when the initial concentration of the ethylhexanoate anion falls below a minimum value necessary to provide adequate protection against corrosion. In the latter case, the presence of cation aluminum in the final reaction mixture will indicate that the level of proportion against corrosion was insufficient. The stoichiometry of the reaction of the aluminum cation with ethylhexanoate anion can vary with other refrigerants containing ethylhexanoate. In this case, the minimum amount of aluminum cation necessary to determine a minimum heilhexanoate anion content will also vary and be determined empirically.

EXAMPLE 2 This example illustrates the method of the invention for determining the presence or absence of effective levels of ethylhexanoate anion in different refrigerant solutions. Five solutions were prepared by combining the indicated amounts of the standard solution of the aluminum cation with the refrigerant A as described in Example 1. The solutions were combined so that the resulting mixtures had ethylhexanoate anion and aluminum cations in ratios in the range from 5 to 10. to 0. Table 5 presents the exact proportions of the components used to prepare each solution.

Table 5: Aluminum relations and coolant solution A Solution Molar ratio Weight of the standard solutions Coolant weight Weight of water target EH / Al of the cation Al, (g) A, (g) deionized (g) 1 5.0 20.0 23.7 6.4 2 3.0 20.0 14.3 15.8 3 2.0 20.0 9.5 20.5 4 1.0 20.0 4.8 25.3 5 0.0 20.0 0.0 30.1 To determine the presence or absence of free aluminum cation after mixing and reaction of the components of the solutions mentioned in Table 5, a colorimetric test for aluminum was adapted from a procedure described in Hattfield, WD, " Soluble Aluminum and Heatoxylin Test in Filtered Waters. " Ind. And Egn. Chem., March 1924, p. 233. According to this procedure, the aqueous aluminum cations produce a purple color in the presence of hematoxylin as a color indicator. The test is reported sensitive for aluminum cations in concentrations within the ppmm range. If no aluminum cation is present, the hematoxylin indicator produces a yellow color under the conditions of this test. Each solution in Table 5 was made alkaline with 1.0 g of saturated solution of ammonium carbonate in deionized water. 1.0 g of color indicator solution (0.1 g of hematoxylin in 100 g of deionized water) was then added to each solution shown in Table 5. The resulting mixtures were stirred and allowed to stand for 15 minutes to allow the reaction of the Color indicator with free aluminum cations if present. Next, each solution was acidified to a pH of about 5 by the addition of 10 g of 30% acetic acid and filtered to remove the precipitated aluminum ethylhexanoate that formed when the aluminum standard solution was initially mixed with the refrigerant A Table 6 below shows the color changes observed in the resulting filtrates: Table 6: Colors of the filtrate after the hematoxylin test for free Al + 3 in coolant A solutions (molar ratio EH / Al = 5. A 0) Filtered Color 1 yellow (no color change) 2 yellow (no color change) 3 yellow (no color change) 4 dark purple 5 dark purple These results indicate that there was no aluminum cation present in Nos. 1, 2, and 3 filtrates but there was free aluminum cation in filtrates Nos. 4, and 5. In addition, the results indicate that there was enough ethylhexanoate in the original mixture Nos, 1, 2, and 3 to completely eliminate all the aluminum cation added to these mixtures, but in mixtures Nos, 4 and 5 there was insufficient ethylhexanoate present to react completely with all the aluminum cation added. To further define the sensitivity of the test to the variation of the aluminum cation content and the ethylhexanoate anion content, five additional reaction solutions were prepared with initial molar proportions EH / Al in the range from 2.0 to 1.0. Table 7 shows the amount of each component used to prepare the five solutions.

Table 7: Aluminum relations and coolant solution A Solution Molar ratio Weight of Water Weight of target water EH / To deionized refrigerant standard solution of cation Al, (g) A, (g) (g) 1 2.0 20.0 9. 6 20.5 2 1. 6 20.0 7.7 22.4 3 1.4 20.0 6.7 23.4 4 1.2 20.0 5.8 24.3 1.0 20.0 4.9 25.4 As with the solutions described in Table 5, each solution was buffered with ammonium carbonate solution, treated with hematoxylin indicator solution and rested for 15 minutes before acidification and filtration. After filtration, the following colors of the resulting filtrates were observed: Table 8: Colors of the filtrate after the haematoxylin color test for free Al + 3 in mixtures of the refrigerant A solution (molar ratio EH / Al = 2 to 1) Filtered Color 1 yellow (no color change) 2 light purple 3 purple 4 dark purple 5 dark purple The results in Table 8 show that filtrate No. 1 was yellow but filtrates Nos. 2, 3, 4 and 5. showed increasing purple coloration indicating the presence of free aluminum cation in all these solutions with aluminum concentrations increasing as the molar ratio EH / Al decreased from 1.6 to 1.0 in all series. The test indicates that with the filtrate of solution No. 1 of Table 7 (molar ratio EH / Al = 2), sufficient anion ethylhexanoate had been added to the original solution to completely exhaust all added aluminum cations. For each of the other filtrates, insufficient ethylhexanoate anion had been added to completely remove all the added aluminum cation. From the color variations in the series, it can be concluded that as the concentration of ethylhexanoate anion was reduced, the aluminum cation concentration increased proportionally. The results in Tables 6 and 8 are summarized in Table 9 as follows: Table 9: Summary: Results of the hematoxylin color test on mixtures of aluminum cation and refrigerant A Molar ratio Final concentration of Al color of the filtrate after target EH / Al predicted (moles / 1) of the hematoxin test (from table 3) 5.0 0.0 yellow 3.0 0.0 yellow 2.0 0.0 yellow 1.6 0.09 light purple 1.4 0.20 purple 1.2 0.31 purple dark 1.0 0.43 dark purple 0.0 1.0 dark purple As shown by comparison in Table 9 with the predicted compositions mentioned in Table 4, there is an agreement of the predicted presence of the aluminum cation based on the demonstrated stoichiometry of the aluminum-ethylhexanoate reaction with the observed purple color change which indicates the presence of aluminum cation.

EXAMPLE 3 This example illustrates the colorimetric test to determine the level of ethylhexanoate carried out in refrigerant antifreeze / refrigerant Havoline Extended Life (refrigerant B) available commercially from Texaco Lubricant Company. The partial composition of the refrigerant B is set forth in Table 10 as follows: Table 10: Composition of coolant B Component Quantity,% by weight Potassium ethylhexanoate 3.26 * Dye 0.10 * Antifoam 0.06 * As ethylhexanoic acid; present in ethylene glycol.

In contrast to the refrigerant A used in Examples 1 and 2, the refrigerant B contains the conventional antifoam and dye refrigerants in addition to the corrosion inhibitor ethylhexanoate. The dyes present in coolant B will interfere with the interaction of the hematoxylin indicator with the free aluminum cation. This interference tends to obscure the development of the purple color of the aluminum-hematoxylin complex that develops to indicate the presence of the free aluminum cation. This example demonstrates that such color interference can be overcome by increasing the concentration of the color indicator on which it is used in Example 2. Four blends were prepared using standard solutions of 2% aluminum nitrate, coolant B, water solution and aluminum carbonate, all of which have been described above, with hematoxylin color indicator solutions prepared in higher concentrations. The solutions of the color indicator were prepared with a content from 5 to 10 times the content of the hematoxylin indicator of the solutions used in Example 2. The compositions of the four mixtures are presented in Table 11.

Table 11: Colorimetric test solutions for the level of the ethylhexanoate anion in coolant B Mix Solution DEX-CCOL, Deionized Water, Buffer Standard solution of Al (g) (g) '' (g? '' Indicator, (cf) 1 10.0 2.5 12.5 2 10.0 5.0 10.0"l. O 0.5 3 10.0 2.5 12_5 1.0 1.0 4 10.0 5.0 10.0 1.0 1. 0 Mixtures Nos. 1 and 2 were prepared using five times the color indicator, and Mixtures Nos. 3 and 4 were prepared using 10 times the color indicator, of which was used in Example 2. Mixtures Nos. 2 and 4 were prepared with a molar ratio EH / Al of 2.1. Since these mixtures contain ethylhexanoate anion in excess of the stoichiometry of the reaction of 1.75 described in Examples 1 and 2, these two solutions will not contain any free aluminum cation after the reaction. After mixtures Nos 1 and 3 were prepared with a molar ratio EH / Al of 1.05. These two mixtures contain insufficient ethylhexanoate anion to fully react with all the added aluminum cation. The mixtures were allowed to stand for 15 minutes after the preparation and then filtered. The color of the resulting filtrates is given in Table 12.

Table 12: Effect of hematoxylin concentration on appearance in the colorimetric test Filtering Color 1 purple 2 orange 3 purple 4 pink These results show that filtrates Nos. 1 and 3, which contained less than the stoichiometric amount of the ethylhexanoate anion needed to fully react with and remove all of the added aluminum cation, provide a positive purple color. for aluminum. Filters Nos. 2 and 4, which contained ethylhexanoate anion in excess of that necessary to completely remove all aluminum cation added from the solution, provided a negative (non-purple) test. However, unlike the negative aluminum test presented in Tables 6 and 8 that were yellow, these negative tests showed colors in the range from orange to pink. This coloration was due to the increased content of the color indicator. of the filtrate and the dyes present in the refrigerant ~ B. Even with the increased content of the color indicator and the dyes, the purple color of the positive tests can be clearly distinguished from the colors of the negative test.

Claims (16)

1. A method for determining the presence or absence of an inhibiting level of carboxylate anion corrosion in engine coolant used which consists of: a) obtaining a known amount of engine coolant as a representative sample thereof, the sample containing a level of carboxylate anion to be determined; b) adding a certain amount of an aluminum cation source to the sample, the aluminum cation forming a complex with the carboxylate anion to form an insoluble aluminum-carboxylate complex, with free aluminum cation present in the sample when the level of carboxylate anion in it is below an effective amount, corrosion inhibitor, and there is no free aluminum cation present in the sample when the level of carboxylate anion is in an effective amount to inhibit corrosion; c) adding a colored indicator to the sample in a complex irreversibly colorful with any free aluminum cation present therein at a pH that gives rise to the colorful complex, the sample being adjusted within this pH if necessary to allow the formation of the colorful complex; and d) observe the color of any complex that may have formed between the free aluminum cation and the color indicator to determine the level of carboxylate anion in the sample, the sample being adjusted to a different pH if necessary in order to remove any color that may have resulted from the presence of excess color indicator in the sample.

The method of claim 1, wherein the carboxylate anion is selected from the group consisting of the alkali metal salt and the ammonium salt of an aliphatic carboxylic acid.

3. The method of claim 2, wherein the carboxylate anion is ethylhexanoate anion.

4. The method of claim 1, wherein the source of aluminum cation is selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate and its hydrates.

The method of claim 1, wherein the color indicator is selected from the group consisting of hematoxylin, Eriochrome Cyanine R, aurintricarboxylic acid, Pantachrome Blue Black R, and Alizarin S.

6. A method for determining the presence or absence of a corrosion inhibiting level of ethylhexanoate anion in aqueous engine coolant, used which consists in: a) obtaining a known amount of engine coolant as a representative sample thereof, the sample containing a level of ethylhexanoate anion to be determined; b) add a certain amount of an aluminum cation source to the sample, the aluminum cation forming a complex with the aluminum-ethylhexanoate anion to form an insoluble aluminum-ethylhexanoate complex, with free aluminum cation present in the sample when the anion level ethylhexanoate therein is below an effective amount, to inhibit corrosion, and there is no free aluminum cation present in the sample when the level of ethylhexanoate anion is in an effective amount to inhibit corrosion; c) adding hematoxylin to the sample that forms an irreversible colorful complex with any free aluminum cation present therein at a pH greater than 7, the pH of the sample being the sample adjusted if necessary to allow the formation of the colorful complex; and d) observe the color of any complex that may have formed between the free aluminum cation and the haematoxylin to determine the _____notice. ethylhexanoate anion in the sample, the sample being acidified to a pH of 7 or less to remove any color that may have resulted from the presence of excess hematoxylin in the sample.

7. A test kit to determine the presence or absence of a corrosion inhibiting level of the carboxylate anion in a representative sample of engine coolant used consisting of a source of aluminum cation and a color indicator that forms an insoluble complex in water with the aluminum cation.

8. The equipment of claim 7, wherein the aluminum cation source is selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum nitrate and its hydrates.

9. The kit of claim 7, wherein the color indicator inhibitor is hematoxylin.

10. The equipment of claim 7, further comprising a quantity of base and / or acid with which the pH of the refrigerant sample is adjusted.

11. The equipment of claim 9, further comprising a quantity of base and / or acid with which the pH of the refrigerant sample is adjusted.

12. The apparatus of claim 7, further comprising a device for obtaining a sample of engine coolant and a device for maintaining a precise volume of the coolant.

The equipment of claim 12, wherein the device for obtaining a sample of engine coolant is a pipette or syringe.

The equipment of claim 12, wherein the device for maintaining the precise volume of refrigerant is a flask or specimen.

15. The equipment of claim 12, further comprising a filtration unit.

16. The kit of claim 15, wherein the filtering device includes a funnel and filter paper.